The Descent Imager / Spectral Radiometer during the Descent of Huygens
onto Titan on January 14, 2005
Erich Karkoschka, University of Arizona, the DISR Team, NASA, ESA
Copyright 2006/2016 University of Arizona
The movie shows the operation of the DISR camera on-board the Huygens
probe during the descent onto Titan. The almost 4-hour long operation
of DISR is shown in less than five minutes in 40 times actual speed up
to landing and 100 times actual speed thereafter.
The big circle displays the view from Huygens over the bottom hemisphere
including part of the upper hemisphere. As DISR takes images, the
mosaic of Titan's surface builds up. Six small white dots mark the four
cardinal directions, the nadir (straight down), and the landing site.
The lower left corner displays the trajectory of Huygens viewed from
the south. A scale bar indicates the size of Mount Everest for
comparison. Colored arrows point to the sun and to Cassini, which
relayed the data to Earth. The zig-zag of the green trajectory is
caused by unexpected variations of the wind speed.
The left side displays the Huygens probe, showing large, unexpected
parachute motions. A scale bar gives the size of an average person.
To the lower right of the big circle is a compass displaying the
directions to the sun and Cassini. A green arrow shows the changing
viewing direction as Huygens rotated. While Huygens was designed to
spin counterclockwise, it stopped and started spinning clockwise.
To the upper right of the big circle is a clock giving Universal Time
(Greenwich Mean Time) on January 14, 2005. Also listed is the Mission
Time that starts with the deployment of the first parachute.
After touch down on Titan's surface, the main display changes to the
view from DISR in the latest raw images (center) and combined processed
images (right). To facilitate judging the size of the rocks, a scene
from the moon at similar scale is added on the left. The brightness
of images changes with changing exposure times.
The right side of the screen displays detailed information about
parameters of DISR and Huygens: altitude, speed, wind speed, air
pressure, air temperature, and the temperature measured at the optics
and the CCD detector of DISR.
Further down is a counter for the number of images taken. DISR had
a down-looking high and a medium resolution imagers, a side looking
imager operated in two different modes, full image and double strip,
and a solar aureole imager looking up. The timing of each exposure is
shown by a colored dot flashing to the left of each exposure counter.
The viewing direction is shown at right by a colored flashing area in
the circle. The active part of DISR flashes in the same color in the
top left corner. The little dot to the right of the red circle
indicates the direction to the sun for instruments viewing the sky.
Further down is a summary of spectroscopic exposures. DISR had two
visible and two infrared spectrometers, one each looking up and down.
Current spectra are displayed with wavelength increasing to the right.
Dark methane bands appear in the spectra as Huygens sinks into the lower
atmosphere where methane is concentrated. After landing, the surface
lamp provides illumination even where methane blocks out sunlight. The
lamp's large golden reflector is shown in the top left corner. The down
looking visible spectrometer was an imaging spectrometer, and the imaged
parts of Titan are visible as blue flashing lines.
DISR had up and down looking violet photometers. The recorded
brightness levels are indicated by violet squares.
Right below, the red square shows the brightness of the sun measured
by the sun sensor until the sun was fainter than the detection limit.
Further down is a counter of calibration exposures. Right below,
the modest amount of DISR data transmitted is constantly updated.
The graph further down displays the signal strength received by Cassini,
modulated mostly by the rotation of Huygens. The Huygens mission ended
when Cassini went below the horizon as seen from Huygens.
The very bottom lists the number of rotations of Huygens. Rotations
begins with DISR looking toward the sun. The rotational rate is listed
and indicated by the length of the green bar. The rotational rate was
unexpectedly unstable after deployment of the last parachute.
Sound was added to mark various events. The left speaker follows the
motion of Huygens. The pitch of the tone indicates the rotational
speed. Vibrato indicates vibration of the parachute. Little clicks
indicate the clocking of the rotation counter. Noise corresponds to
heating of the heat shield, to parachute deployments, to the heat
shield release, to the jettison of the DISR cover, and to touch down.
The sound in the right speaker follows DISR data. The pitch of the
continuous tone goes with the signal strength. The 13 different chime
tones indicate activity of the 13 components of DISR. The counters at
the top and bottom of the list get the high and low notes, respectively.
All parts of DISR worked together as programmed, creating a harmony.